By Daniel Stern
DVN Global Editor
Our researchers, practitioners and regulators in the lighting world spend a great deal of time and energy focusing on headlamp photometric specifications. There is now about sixty years' worth of research and writing comparing US vs. ECE photometric stipulations from numerous perspectives, looking at the effects on seeing and glare of proposed changes to the specifications, and just plain arguing over which is the right way and which is the wrong way to do it. A lot of this literature is of great utility for answering various questions definitively; one such piece of clear knowledge is that vertical aim is a primary determinant of headlamp safety performance. This stands to basic reason for most of us; even the best headlamp is dangerous and ineffective if it is improperly aimed, and a low-performance headlamp aimed correctly will usually give better safety performance than a high-performance headlamp aimed improperly. (See DVN report published in 2008 at www.DrivingVisionNews.com )
But what do we mean by "proper" aim? The easy answer is to refer to the regulations prevailing in whatever jurisdiction, and a great deal of the applicable literature sets the studied headlamps to their intended aim (US aim for US headlamps, ECE aim for ECE headlamps) as a matter of standardising the test conditions. But following those regulations just assures legal aim, not necessarily optimal aim. Philosophy plays a major part; traditionally in the US the aim specification—by law and by tradition—has been set with maximum seeing distance in mind, and not much attention paid to glare. European countries, in contrast, have long tended to prioritise glare control on low beam with perhaps not enough attention paid to seeing distance. A motorist seeking to have his headlamps adjusted in a European country will generally leave the workshop with the lights aimed low; this is regarded as a "safe" aim by dint of glare control. (A driver seeking to have his headlamps correctly adjusted in North America is almost certainly out of luck, but that is a subject for another discussion.)
